President Barack Obama said the U.S. government took a cautious approach to allegations the Russians had hacked Democratic Party officials before the election out of concern that the issue would escalate or become politicized.

"I wanted to make sure we were playing this thing straight," Obama said Friday at his final end-of-the-year news conference at the White House, defending his administration against criticism that it didn’t more aggressively combat the hacking.

Barack Obama holds a year-end press conference on Dec. 16.

Photographer: Saul Loeb/AFP via Getty Images

"My principal goal leading up to the election was making sure the election itself went off without a hitch, it was not tarnished, and it did not feed any sense in the public that somehow tampering had taken place with the actual process of voting," Obama said. "And we accomplished that."

The Central Intelligence Agency has reportedly determined that Russian president Vladimir Putin directed the hack in an effort to buoy the candidacy of Republican Donald Trump, enraging many Democrats who believe the election was unfair. Obama called on Trump, who has openly challenged the administration’s determination of Russian culpability, to back a nonpartisan independent probe of the election and the hacks. The president also challenged Americans who support Putin or who doubt U.S. intelligence agencies, warning that such thinking left the nation susceptible to foreign meddling.

"Our vulnerability to Russia or any other foreign power is directly related to how divided, partisan, dysfunctional, our political process is," Obama said.

Putin’s Involvement

Obama declined to say that Putin personally was involved in the hacking but said: "Not much happens in Russia without Vladimir Putin." He said he had high confidence Moscow was responsible for attacks on the e-mails of both the Democratic National Committee and Hillary Clinton’s campaign chairman, Jon Podesta. But he said the government would not be able to provide classified evidence of Russia’s involvement that might reveal the U.S. intelligence community’s sources and methods.

Russia backed off the hacking after Obama personally warned Putin against further cyberattacks during a visit to China in September, the president said. But by then, the Democratic e-mails were in the hands of Wikileaks, which released them over the course of the general election campaign, prolonging the damage to Clinton.

Obama declined to say that the hacks cost her the election.

"I’m gonna let all the political pundits in this town have a long discussion about what happened in this election," he said. "I don’t think she was treated fairly during the election. The coverage of her, and the issues, was troubling."

U.S. Retaliation

Still, Obama vowed that the U.S. would respond to Russia in a "thoughtful, methodical way."

"Our goal continues to be to send a clear message to Russia or others not to do this to us, because we can do stuff to you," he said.

The Kremlin has denied involvement in the e-mail leaks, and spokesman Dmitry Peskov told reporters in Tokyo on Friday the U.S. should prove its accusations against Russia.

“Either stop talking about it or finally provide some evidence. Otherwise it looks indecent,” Peskov said in Japan, where Putin is meeting with Japanese leaders.

Clinton told donors at a fundraiser on Thursday that the hacks were partially to blame for her loss to Trump. She said the Russians had sought to “undermine our democracy” through the cyberattacks, which she believed were a result of Putin’s “personal beef” against her.

“Putin publicly blamed me for the outpouring of outrage by his own people, and that is the direct line between what he said back then and what he did in this election,” the Democrat said, according to a recording of the event obtained by the New York Times. She also said that Federal Bureau of Investigation Director James Comey’s Oct. 28 letter disclosing a new investigation of e-mails from her time as secretary of state damaged her with swing-state voters days before the election. The two factors were “unprecedented,” Clinton said.

Trump Complaints

The renewed focus on the Russian hack has prompted complaints from the Trump transition team that the White House is attempting to undermine the Republican’s victory. The administration announced late last week plans to issue a report on electoral cyberattacks before Obama leaves office on Jan. 20.

The White House and Trump team have traded escalating insults in recent days that threaten the detente between Trump and Obama, who has sought a working relationship with his successor partially in a bid to preserve some of his policies. It’s also blurred traditional party lines in Washington, with some Republicans expressing alarm over Russia’s attempts to influence an election ultimately won by their nominee and some Democrats upset the White House didn’t more aggressively confront the Kremlin before Election Day.

In a tweet early Friday, Trump tried to return attention to revelations in e-mails revealed by the alleged Russian hack.

“Are we talking about the same cyber-attack where it was revealed that head of the DNC illegally gave Hillary the questions to the debate?” Trump wrote. He was referring to e-mails stolen from Clinton campaign Chairman John Podesta, which indicated that a Democratic official and CNN analyst, Donna Brazile, had obtained questions to be asked in debates during the Democratic primary and relayed them in advance to Clinton’s campaign.

‘Playing Politics’

Senator Ron Johnson, a Wisconsin Republican and vocal Trump supporter, said Friday that Democrats were “certainly playing politics” with the situation. He told CNBC that he had been denied a request to be briefed by CIA officials on Russia’s involvement, and that he had not seen evidence Russia was responsible.

“I’m assuming that’s true, but who did they hack?” Johnson said. “Was it the DNC? Was it John Podesta? I haven’t seen that evidence.”

Senator Richard Burr, chairman of the Senate Intelligence Committee, said Friday that his panel will continue to investigate Russian hacking of U.S. interests, including the breaches of political groups before the 2016 election. In a statement, the North Carolina Republican said that the committee would hold hearings in the new year, interviewing officials from both the Obama and Trump administrations.

Burr defended “the hard-working, patriotic Americans” working for U.S. intelligence agencies, saying “they check politics at the office door and focus on their mission.” Trump’s transition team last week ridiculed the intelligence agencies for their claims of foreign interference in the election, and drew comparisons with the erroneous findings that Iraq’s Saddam Hussein had weapons of mass destruction before the U.S. invasion in 2003.

‘Deeply Broken’

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Obama said he hoped the incident would give the nation reason to reflect on the state of politics, calling for Americans to place country above party. He said Democrats need to engage in self-reflection and campaign in areas where they are perceived as "latte-sipping, politically correct" coastal elites. He acknowledged his own failures in translating his personal popularity to broad success for his party.

Democrats must "make sure we’re showing up in places where I think Democratic policies are needed, where they’re helping, where they’re making a difference, but people don’t feel as if they’re being heard," Obama said.

"What I was able to do in my campaigns I wasn’t able to do during the midterms," Obama said. The "coalition I put together didn’t always turn out to be transferable."

Bitterness lingers among top Clinton allies upset with the way members of the Obama administration handled the closing weeks of the campaign. Podesta, a former senior counselor to Obama, wrote in a Washington Post commentary published Friday that the FBI had been more scrupulous in its investigation of Clinton’s e-mails than it was in investigating the DNC hacks.

“Comparing the FBI’s massive response to the overblown e-mail scandal with the seemingly lackadaisical response to the very real Russian plot to subvert a national election shows that something is deeply broken at the FBI,” Podesta said.

Obama on Friday defended law enforcement professionals, saying they faced a difficult task when their investigations intersected with politics.